1. Field of the Invention
The present invention is directed to an anti-distortion insert to provide threaded attachment to a panel. More specifically, the present invention is directed to an anti-distortion insert for threaded fastening of optical elements to a honeycomb panel.
2. Background Information
Elements of an optical system are often mounted together on a common flat panel. Threaded inserts are embedded in the panel at predetermined positions so that the optical elements may be bolted to the common flat panel in a straightforward manner.
Referring to FIG. 1, a cross-sectional view is shown of a threaded insert 10 that is bonded to a honeycomb panel 12 by epoxy resin 14. The insert 10 is embedded all the way through the panel 12. The threaded bore 16 of the insert 10 is useful for fastening elements of an optical system to the panel 12.
Referring to FIG. 2, a cross-sectional view is shown of a threaded insert 18 that is embedded only partially through a honeycomb panel 20. The insert 18 is bonded to the panel 20 by epoxy resin 22. The threaded bore 24 of the insert 18 is useful for fastening elements of an optical system to the panel 20.
Honeycomb panels (i.e., having a honeycomb core structure) have been developed that have very low thermal distortion properties in the lateral plane (i.e., the plane of the flat panel). As a result, the elements of the optical system that are affixed to a honeycomb panel maintain a consistent position and orientation in the lateral plane, despite temperature gradients that may develop across the honeycomb panel. However, thermal expansion and contraction in the transverse direction (i.e., perpendicular to the plane of the flat panel) remains a problem for honeycomb panels.
The amount of expansion or contraction of the panel per unit of temperature in the transverse direction is called the transverse (or xe2x80x9cthrough-the-thicknessxe2x80x9d) Coefficient of Thermal Expansion. The transverse Coefficient of Thermal Expansion (CTETRANS) of a honeycomb panel in the vicinity of a conventional bonded insert is primarily a function of the material forming the core of the panel, the material forming the insert, and the type and amount of the adhesive used to bond the insert to the panel. This may be expressed generally as
CTETRANSxcx9cK1xc2x7CTEPANEL+K2xc2x7CTEINSERT+K3xc2x7CTEBONDxe2x80x83xe2x80x83(1)
where CTEPANEL is the coefficient of thermal expansion of the panel core material in the transverse direction, CTEINSERT is the coefficient of thermal expansion of the insert material, CTEBOND is the coefficient of thermal expansion of the material bonding the insert to the panel, and K1, K2, and K3 are each constants.
For a conventional insert, the CTETRANS at the insert can be substantial, causing the optical component mounted to the panel at that location to undergo an unacceptably high transverse deflection as a result of a temperature change.
To attempt to minimize CTETRANS, it has been proposed to make the inserts of a material that has a low CTE and to increase the mass of the inserts. Although this would tend to lower the overall CTETRANS, it is not an acceptable alternative for applications where minimizing weight is critical. The panel generally has dozens of inserts. Making substantial increases in the mass of each of the inserts would add up to a large mass increase in the aggregate. Such a large mass increase would be problematic, for example, in a spacecraft where mass must be minimized for launch.
It has also been proposed to manufacture the honeycomb panel using a graphite core with improved dimensional stability. However, this is not a satisfactory solution either, because (assuming a sufficiently stable graphite core could be discovered) the thermal dimension changes caused by the bonding material would still contribute to a CTETRANS of substantial size.
Thus, what is needed is an insert, for use with honeycomb panels, which will isolate an optical component mounted thereon from thermal expansion and contraction of the honeycomb panel and any bonding material used to bond the insert to the panel.
Furthermore, even if an optical component could be perfectly isolated from the thermally induced dimension changes of the honeycomb panel and the bond material, this does not solve the entire problem. That is because the insert itself also expands and contracts as a function of temperature. Accordingly, the insert also contributes to CTETRANS.
Thus, what is also needed is an insert that will compensate for its own thermal expansion and contraction, so as to minimize thermally-caused deflection of an optical component mounted thereon.
It is an object of the present invention to provide an interface point to a honeycomb panel that has a very low CTETRANS irrespective of the CTE of the honeycomb panel in the transverse (through-the-thickness) direction.
It is also an object of the present invention to provide a honeycomb panel threaded insert that isolates an optical component mounted thereon from thermal expansion and contraction of the honeycomb panel and any bonding material used to bond the insert to the panel.
It is an additional object of the present invention to provide a threaded insert that compensates for its own thermal expansion and contraction, so as to minimize thermally-caused deflection of a component mounted thereon.
It is a further object of the present invention to provide a mounting panel for mounting components, wherein the attachment points for mounting have a very low CTETRANS irrespective of the CTE of the mounting panel in the transverse (through-the-thickness) direction.
Some of the above objects are achieved by a fastener for providing isolation from thermal expansion and contraction. The fastener has a sleeve and a post. The sleeve has a positioning pad projecting from its interior surface. The post is attached to the inside of the sleeve and is axially positioned inside the sleeve by the positioning pad. The post is substantially isolated by the sleeve from thermal expansion and contraction external to the fastener.
Other of the above objects are accomplished by an insert for use with a honeycomb panel. The insert has a sleeve and a post. The sleeve has a positioning pad projecting from its interior surface. The post is attached to the inside of the sleeve and is axially positioned inside the sleeve by the positioning pad.
Another of the above objects is accomplished by mounting panel for mounting optical elements via threaded engagement. The mounting panel has a honeycomb panel with plural threaded inserts imbedded in the honeycomb panel at predetermined locations. The inserts each have a sleeve and a post. The sleeves each have a positioning pad projecting from their interior surfaces. The posts are attached to the inside of their respective sleeves and are axially positioned inside the sleeve by the positioning pad.
Some of the above objects of the present invention are also achieved by a one piece unitary insert for use with a honeycomb panel. The insert has a sleeve portion and a post portion. The post portion is surrounded by the sleeve portion and cantilevered with respect to the sleeve portion from a meeting point axially positioned inside the sleeve portion.
According to one embodiment of the present invention, the insert has two parts, a sleeve and a post that attaches to the inside of the sleeve. The exterior surface of the sleeve is bonded to the panel and has a positioning pad on its interior surface. The post has a threaded engagement with the sleeve, and is axially positioned inside the sleeve by the positioning pad.
According to another embodiment of the present invention, the insert is formed of a single piece having a sleeve portion and a post portion inside the sleeve portion. The exterior of the insert is bonded to the panel. The point at which the post portion and the sleeve portion meet is the meeting point. The meeting point location is selected so as to isolate the post portion from thermal expansion effects of the panel and bonding material, and to compensate for the thermal changes in the post portion itself.